System and method for biomass combustion

ABSTRACT

Disclosed is a system and method for the combustion of biomass material employing a swirling fluidized bed combustion (SFBC) chamber, and preferably a second stage combustion carried out in a cyclone separator. In the combustion chamber, primary air is introduced from a bottom air box that fluidizes the bed material and fuel, and staged secondary air is introduced in the tangential direction and at varied vertical positions in the combustion chamber so as to cause the materials in the combustion chamber (i.e., the mixture of air and particles) to swirl. The secondary air injection can have a significant effect on the air-fuel particle flow in the combustion chamber, and more particularly strengthens the swirling flow, promotes axial recirculation, increases particle mass fluxes in the combustion chamber, and retains more fuel particles in the combustion chamber. This process increases the residence time of the particle flow. The turbulent flow of the fuel particles and air is well mixed and mostly burned in the combustion chamber, with any unburned waste and particles being directed to the cyclone separator, where such unburned waste and particles are burned completely, and flying ash is divided and collected in a container connected to the cyclone separator, while dioxin production is significantly minimized if not altogether eliminated. The system exhaust is directed to a pollutant control unit and heat exchanger, where the captured heat may be put to useful work.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/056,179 entitled “SYSTEM AND METHOD FOR BIOMASS COMBUSTION” filedwith the U.S. Patent and Trademark Office on Feb. 29, 2016, now U.S.Pat. No. 10,253,974 issued on Apr. 9, 2019, which is based upon andclaims benefit of copending U.S. Provisional Patent Application Ser. No.62/121,843 entitled “Method and Design of the Ultra-Clean MobileCombustor for Waste Biomass and Poultry Litter Disposal,” filed with theU.S. Patent and Trademark Office on Feb. 27, 2015 by the inventorherein, the specification of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to systems and methods for fluidized bedcombustion, and more particularly to a fluidized bed combustion systemand method optimized for burning biomass wastes and poultry litter in anenvironmentally-friendly manner.

BACKGROUND OF THE INVENTION

The consolidation and industrialization of the poultry industry over thelast 50 years has resulted in highly concentrated regional poultryoperations. Traditionally, farmers managed the manure or litterassociated with poultry production by spreading it on fields. However,as the industry consolidated, operations became highly regionallyconcentrated, and cropland diminished, this waste disposal method becameless viable. For example, in the Maryland-Delaware region, 523 millionchickens are now produced annually, generating approximately 42 millioncubic feet of chicken waste each year, such that chickens outnumberpeople in the region by as much as 400 to 1. This high concentration ofwaste causes eutrophication (e.g. nitrogen, phosphorus), particularlyalong the shores of the Chesapeake Bay, the largest estuary system inthe United States, creating an urgent need for efficient, clean,environmentally friendly chicken waste disposal approaches.

The United Nations and The U.S. Federal Government have identifiedagriculture as the biggest user of water and a major polluter of water.In fact, agriculture has been identified as the single largest source ofpollutants for rivers, lakes, and estuaries in the U.S. Theindustrialization of agriculture has resulted in such highconcentrations of animal waste that conventional disposal methods are nolonger adequate or viable (e.g. spreading on fields). Thus, there is anurgent need for environmentally safe and economically viable approachesto disposing of agricultural waste. This need in combination with globaldemand for clean, low-cost, renewable energy has fueled interest inbiomass-to-energy conversion technologies, including for use indisposing of high concentrations of animal waste, which approach becomeseven more appealing given recently implemented regulations that prohibitthe use of chicken litter as fertilizer on significant acreage. However,due to the low energy density of biomass, the economics ofbiomass-to-energy operations have been challenging (i.e., fuelcollection and transportation costs can be high relative to energydensity; high moisture content adds to transportation costs and reducesburn efficiencies). Thus, there remains a need for solutions that canreduce the cost of converting biomass to energy and/or increase theefficiency of the combustion process.

Fluidized bed combustion systems are often used for burning biomassfuel. Most of the existing fluidized bed combustion apparatus known tothe inventor have only a single level secondary injection of air in thefixed tangential direction to facilitate a turbulent or swirling flow,as shown in U.S. Pat. No. 5,105,917 to Harada et al., and in U.S. Pat.No. 8,161,917 to Yang et al., the specifications of which areincorporated herein by reference in their entireties. Certain systemsdisclose multiple secondary air supply ports, such as the system shownin European Patent Publication No. 0 458 967 A1. Still other systemsdisclose methods for incinerating waste using a two-level swirling flowfluidized bed without tangential flow for suppressing re-synthesis ofdioxins produced during incineration and the removal of a suspendedparticulate material, such as the system disclosed in International PCTPublication No. WO/2010/010630. The specifications of each of theforegoing references are incorporated herein by reference in theirentireties. However, widespread commercial acceptance of such priorsystems has been lacking, due to an inability to reach sufficiently highcombustion efficiencies and minimization of noxious emissions. Thus,there remains a need in the art for fluidized bed combustion systems andmethods capable of efficiently and cleanly disposing of biomassmaterials.

SUMMARY OF THE INVENTION

Disclosed is a system and method for ultra-clean and preferably mobilecombustion, particularly configured for burning biomass and poultrylitter in an environmentally friendly manner (i.e., so as to reduceemissions of pollutants), which system and method provides highcombustion efficiency using equipment of compact design and that is easyto operate.

In accordance with certain aspects of an embodiment of the invention,the system carries out preferably a two-step combustion process, namely,a first stage combustion carried out in an advanced swirling fluidizedbed combustion (SFBC) chamber, and a second stage combustion carried outin a cyclone separator. In the combustion chamber, primary air isintroduced from a bottom air box that fluidizes the bed material andfuel, and staged secondary air is introduced in the tangential directionand at varied vertical positions in the combustion chamber so as tocause the materials in the combustion chamber (i.e., the mixture of airand particles) to swirl. The secondary air increases the residence timeof the particle flow. The turbulent flow of the fuel particles and airis well mixed and mostly burned in the combustion chamber. Any waste andparticles that remain unburned in the combustion chamber are directed tothe cyclone separator, where such unburned waste and particles areburned completely, and flying ash is divided and collected in acontainer connected to the cyclone separator, while dioxin production issignificantly minimized if not altogether eliminated. The collected ashand char may optionally be used as fertilizer. The system exhaust, inthe form of high temperature flue gas, is directed to a pollutantcontrol unit and heat exchanger, where the captured heat may be put touseful work, such as by generating steam for delivery to a turbine,powering a Sterling engine, or such other energy generation devices asmay be apparent to those skilled in the art, or for direct heating ofprocess materials, such as water, feed stock (for drying the same), orthe like, or such other direct heat application processes as may beapparent to those skilled in the art.

The system and method set forth herein have the potential tosignificantly improve the economics of biomass-to-energy operations, bydramatically improving the efficiency of the combustion process whilereducing capital and operating costs. The single chamber design incomparison to the classic combustor system with multiple chamberscontributes to lower capital costs. This novel system yields a moreefficient burn rate and less solid and gaseous waste than conventionalsystems for biomass waste disposal.

Relative to other biomass combustion systems, the system and methoddisclosed herein is expected to have a higher electrical output, lowercapital cost, lower maintenance costs, and greater flexibility regardingfuel sources and conditions. Thus, the system and method set forthherein has the potential to significantly improve the economics ofbiomass-to-energy operations. In a particularly preferred embodiment, asystem and method operating in accordance with the disclosure hereinwould have a commercial electrical power rating of 50 MWe, would carry acapital cost of $3,000-$3,200 per kW, and would carry operating andmaintenance costs of $15-$20/ton of feed, thus offering a clean, highefficiency, and affordable method to dispose of biomass and poultrylitter while generating energy.

In accordance with certain aspects of an embodiment of the invention, asystem for fluidized bed combustion is disclosed comprising a combustionchamber, the combustion chamber further comprising: a primary airdistribution and delivery system configured to provide vertical airflowthrough the combustion chamber; and a secondary air distribution anddelivery system configured to provide a plurality of verticallydisplaced, horizontally aligned, tangential airflows in the combustionchamber; and a biomass feeder in communication with an interior of thecombustion chamber and positioned to deliver biomass material to theinterior of the combustion chamber at a location above the primary airdistribution and delivery system and below the secondary airdistribution and delivery system.

In accordance with further aspects of an embodiment of the invention, amethod for fluidized bed combustion is disclosed, comprising the stepsof: providing a combustion chamber, the combustion chamber furthercomprising: a primary air distribution and delivery system configured toprovide vertical airflow through the combustion chamber; and a secondaryair distribution and delivery system configured to provide a pluralityof vertically displaced, horizontally aligned, tangential airflows inthe combustion chamber; providing a biomass feeder in communication withan interior of the combustion chamber and positioned to deliver biomassmaterial to the interior of the combustion chamber at a location abovethe primary air distribution and delivery system and below the secondaryair distribution and delivery system; directing biomass from the biomassfeeder to the combustion chamber; directing a vertical primary airflowinto the combustion chamber and multiple, vertically displacedtangential airflows into the combustion chamber to create a swirlingfluidized bed of biomass particles in the combustion chamber; andmaintaining a biomass feed rate from the biomass feeder, a primaryairflow rate from the primary airflow, and a secondary airflow rate fromthe tangential airflows sufficient to maintain a combustion efficiencyof at least 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the present invention may be betterunderstood by those skilled in the art by reference to the accompanyingdrawings in which:

FIG. 1 is a schematic view of a system for burning biomass in accordancewith certain aspects of an embodiment of the invention.

FIG. 2 is a close-up, cross-sectional view of a combustion chamber usedin the system of FIG. 1.

FIG. 3 is a top, cross-sectional view of the combustion chamber of FIG.2.

FIG. 4 is a side view of primary airflow nozzles for use in thecombustion chamber of FIG. 2.

FIG. 5 is a cross-sectional view a secondary airflow nozzles for use inthe combustion chamber of FIG. 2.

FIG. 6 is a top, cross-sectional view of a cyclone separator used in thesystem of FIG. 1.

FIG. 7 is a flowchart depicting a method for burning biomass inaccordance with certain aspects of an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of a particular embodiment of theinvention, set out to enable one to practice an implementation of theinvention, and is not intended to limit the preferred embodiment, but toserve as a particular example thereof. Those skilled in the art shouldappreciate that they may readily use the conception and specificembodiments disclosed as a basis for modifying or designing othermethods and systems for carrying out the same purposes of the presentinvention. Those skilled in the art should also realize that suchequivalent assemblies do not depart from the spirit and scope of theinvention in its broadest form.

FIG. 1 shows a schematic view of a system for burning biomass inaccordance with certain aspects of an embodiment of the invention,including a combustion chamber 100, air delivery system (shown generallyat 200), a cyclone separator 300, a heat exchanger 400, and exhaustsystem 500. Optionally, the entire system may be housed on a mobilechassis (not shown) so that the system may be moved from site to sitefor processing of biomass at the site of production or collection of thebiomass.

Combustion chamber 100 includes a generally cylindrical housing havingpreferably a metal exterior and a refractory layer on an interiorsurface of the metal exterior. A primary air distribution and deliverysystem 110 is provided in the bottom of the combustion chamber 100, andreceives high pressure air from air delivery system 200, in turndirecting that air toward the top of the combustion chamber in order tovertically distribute the biomass/fuel and diffuse particles throughoutthe column in the combustion chamber 100. Moreover, secondary airdistribution and delivery system 130 includes multiple, verticallydisplaced rows of nozzles, discussed in greater detail below, whichnozzles are configured to provide controllable, multi-angleair-injection at multiple, distinct vertical levels within combustionchamber 100 to provide a swirling flow in the column, which in turnmaximizes combustion throughout the combustion chamber 100.

A fuel feeder 102 is provided adjacent combustion chamber 100, and maybe provided, by way of non-limiting example, a hopper for receivingbiomass, poultry litter, and other materials that might be used for fuelin the combustion chamber 100, and a delivery mechanism 103, such as afeed screw, configured to deliver such biomass/fuel from fuel feeder 102to combustion chamber 100. Such biomass/fuel is delivered intocombustion chamber 100 at a point above primary air distribution anddelivery system 110, and below secondary air distribution and deliverysystem 130. The solid biomass/fuel is supplied tangentially into thecombustion chamber 100, such that no bed material is required. Theairflow from the primary air distribution and delivery system 110 andfrom the secondary air distribution and delivery system 130 act as bothparticle fluidizers and combustion oxidizers. The multiple levels ofnozzles of secondary air distribution and delivery system 130 provideextended swirl flow along with additional air (e.g., oxygen supply).This configuration retains particles in the combustion zone, reducingunburned particles and thus minimizing residual material. The extendedswirling flow generated by the system results in vigorousparticle-to-wall collisions, which increases the residence time andcombustion efficiency of fuel particles in the combustion zone.

A natural gas feed 104 is preferably positioned to feed natural gas intocombustion chamber 100 above primary air distribution and deliverysystem 110. Natural gas is preferably used only to initiate the burn atstartup in order to achieve the initial biomass ignition. Further,monitoring and control subsystem 160 is provided, which preferablyincludes temperature and pressure sensors 162 within combustion chamber100, one or more particulate matter (PM) meters and emissions probes 164capable of monitoring both levels of particulates and gaseous emissions(including NOx, SOx, CO, and CO₂), which sensors and probes are readilycommercially available such that their specific configuration is notaddressed further here. Likewise, those skilled in the art willrecognize that additional process control accessories may be provided asmay be suitable for a particular installation. Monitoring controlsubsystem 100 is also in electrical communication with, and thus isconfigured to provide control signals to, delivery mechanism 103 fromfuel feeder 102 (e.g., by controlling a motor driving a feed screw ofdelivery mechanism 103) to control the amount of biomass/fuel deliveredto combustion chamber 100, to a blower 112 to control the amount of airdelivered through primary air distribution and delivery system 110 andthrough secondary air distribution and delivery system 130, andpreferably to valves 114 to allow independent control of the amount ofair delivered through such systems 110 and 130 with respect to oneanother. Alarm levels may be established for monitored data, which alarmlevels are preferably set by a person using data processing equipment166 responsible for configuring the system. As an alarm relay isactivated, the monitoring and control subsystem 160 is configured todecrease the fuel feeding rate through preferably a variable speedcontroller, reducing such feed rate to a point necessary to have theparticulate matter levels below the set alarm relay levels. Likewise,monitoring and control subsystem 160 controls the amount of airdelivered through primary air distribution and delivery system 110 andthrough secondary air distribution and delivery system 130 (throughcontrol of blower 112 and valves 114 in air delivery system 200) so asto control the burn rate in combustion chamber 100. All of these factorsmay be controlled so as to maintain the safest possible burn rate so asto maintain emissions within a desired range and so as to ensure amaximum efficiency in biomass combustion is maintained.

With continued reference to FIG. 1, exhaust from combustion chamber 100is directed to a cyclone separator 300. As will be discussed in furtherdetail below, any waste and particles that remain unburned in combustionchamber 100 are directed to the cyclone separator 300, where suchunburned waste and particles are burned, and flying ash is divided andcollected in a container connected to the cyclone separator, whiledioxin production is significantly minimized if not altogethereliminated. The collected ash and char may optionally be used asfertilizer. The system exhaust, in the form of high temperature fluegas, is directed from cyclone separator 300 to a heat exchanger 400 andan exhaust system 500 including a pollutant control unit. Heat capturedby heat exchanger 400 may be put to useful work through use of anythermal energy conversion device 420 as may be deemed appropriate for agiven installation by persons of ordinary skill in the art, such as byway of non-limiting example by generating steam for delivery to aturbine, powering a Sterling engine, or such other energy generationdevices as may be apparent to those skilled in the art, or for directheating of process materials, such as water, feed stock (for drying thesame), or the like, or such other direct heat application processes asmay be apparent to those skilled in the art.

FIG. 2 provides a front, cross-sectional view of combustion chamber 100,while FIG. 3 provides a top, cross-sectional view of combustion chamber100. As shown in FIGS. 1-3, combustion chamber 100 includes a primaryair box 116 that receives primary air from blower 112, and directs suchprimary air to primary air distribution and delivery system 110. Primaryair distribution and delivery system 110 directs primary air intocombustion chamber 100, where such primary air receives natural gasthrough natural gas feed 104 and biomass/fuel from delivery mechanism103, both igniting the biomass as it enters combustion chamber 100 andcausing it to flow upward in combustion chamber 100. As such biomassflows upward through combustion chamber 100, it encounters secondary airdistribution and delivery system 130, which in turn comprises two ormore airflow manifolds 132, each of which receives air from air deliverysystem 200. Each airflow manifold 132 directs secondary air to aplurality of secondary air injection nozzles 134 positioned around aninterior circumference of combustion chamber 100. In a particularlypreferred embodiment, four air injection nozzles 134 are provided at acommon height on the interior of combustion chamber 100, and are spacedevenly along the interior circumference of combustion chamber 100 atthat common height. The secondary air injection nozzles 132 control thedirection of the injected secondary air into combustion chamber 100,injecting such secondary air at various angles so as to cause theparticles and air in combustion chamber 100 to achieve a swirling effectso as to increase combustion of the biomass in combustion chamber 100.

As best shown in the top, cross-sectional view of FIG. 3, air nozzles132 a may be provided along an exterior of combustion chamber 100 thatreceive secondary air from airflow manifolds 132, and deliver suchsecondary air to each secondary air injection nozzle 134. Each secondaryair injection nozzle 134 has a first branch that extends radiallythrough both an exterior metal layer 150 of combustion chamber 100 andan internal refractory layer 152 lining an interior of combustionchamber 100. An interior branch of each air injection nozzle 132 isarranged at approximately 90° to each respective first branch so as toposition the outlet of secondary air injection nozzle 134 to directsecondary air tangentially along the interior of refractory layer 152 ofcombustion chamber 100, in turn creating a swirling effect on theinterior of combustion chamber 100.

As shown in the side view of primary air distribution and deliverysystem 110 of FIG. 4, the primary air distribution and delivery system110 includes a plurality of primary nozzles 120, which nozzles 120 areparticularly configured to maximize air distribution at the bottom ofcombustion chamber 100. Each nozzle 120 has a rounded, semi-circularhead 121, a cylindrical branch 122 extending downward from head 121, andan outwardly extending lower branch 123 that has a widening diameter asit extends from cylindrical branch 122 to base portion 124, which baseportion 124 comprises the widest diameter d for each nozzle 120. Baseportion 124 receives air directly from primary air distribution anddelivery manifold 125, which extends horizontally along the bottomportion of combustion chamber 100, receiving air from primary air box116. In certain configurations, a plurality of manifolds 125 may extendhorizontally across the bottom of combustion chamber 100 so as toprovide even distribution of nozzles 120 across the full width ofcombustion chamber 100.

With continued reference to FIG. 4, horizontally extended outlets 126are positioned on each cylindrical branch 122, and upwardly angledoutlets 127 are positioned on each lower branch 123, for feeding airfrom primary air distribution and delivery system 100 into combustionchamber 100. In a particularly preferred embodiment, each primary nozzle120 includes four horizontally extended outlets 126 and four upwardlyangled outlets 127. In a prototype construction implementing the systemand methods described herein (described in greater detail below), atotal of 24 outlets 126 were provided, each having a diameter d of ⅛inch. In an embodiment of the invention, openings formed by horizontallyextended outlets 126 and upwardly angled outlets 127 comprise 2% of theoverall surface area of the primary air distributors.

Similarly, and with reference to the cross sectional view of secondaryair injection nozzles 134 of FIG. 5, both the shape and axial positionof secondary air nozzles 134 are important to providing proper air andmaterial flow within combustion chamber 100. More particularly,secondary air injection nozzles 134 function to change the direction ofthe supplied secondary air so as to cause a swirling flow conditioninside of combustion chamber 100. As mentioned above, sets of preferablyfour, evenly circumferentially spaced secondary air injection nozzles134 are provided at at least two, and preferably three, distinct heightson the interior of combustion chamber 100. In the prototype constructiondescribed above, the bottom-most set of secondary air injection nozzles134 were positioned 34 inches from the bottom of the combustion chamberand primary air distribution manifold 125, with the subsequent highersets of secondary air injection nozzles 134 each evenly spaced 10-11inches above the next-lowest set. In any configuration, the position andnumber of secondary air injection nozzles will generally be determinedby the height of the combustion chamber 100 above air box 116, withhorizontally aligned sets of secondary air injection nozzles 134 beingpositioned equidistant to one another. It has been found that at leastthree horizontal sets of secondary air injection nozzles 134 are mostpreferred in order to ensure that an optimal biomass material residencetime is maintained for the biomass particles undergoing combustion. Thehigher the number of second air injection nozzles 134, the higher theoxygen supply into the combustion chamber 100, which in turn increasesthe swirling effect on the fluidized bed and a resulting high combustionefficiency above 90%. Each secondary air injection nozzle 134 includesinlet 135 that receives secondary air from an airflow manifold 132.Inlet 135 opens into inlet channel 136, which in turn directs secondaryair into a centrally located, circular chamber 137. An interior flowchannel 138 extends from chamber 137, and at a distal end directs theairflow through nozzle outlet 139, which outlet 139 extends at generally90° to a flow axis of both inlet channel 136 and interior flow channel138, in turn introducing air into combustion chamber 100 in a tangentialdirection so as to cause swirling air flow. This configuration has beenfound to provide a swirling air flow from the secondary air injectioninto combustion chamber 100, which in turn forms the particle suspensionlayer and dilution zone within combustion chamber 100. Throughadjustment of the secondary air injection through secondary airinjection nozzles 134 configured in this manner, the axial position ofthe particle suspension layer within combustion chamber 100 can beclosely controlled.

The resulting strong swirling air flow field in combustion chamber 100,in combination with the interaction of centrifugal forces and gravity onthe particles in combustion chamber 100, cause larger particles to bekept in combustion chamber 100 for a significant amount of time, in turncontributing to high combustion efficiency and extremely low emissions.The swirling particle flow in combustion chamber 100 can be described bystochastic trajectory modeling (STM), and the diffusion-kinetics modelcan be used for predicting fuel materials depletion during thecombustion process to describe the residence time of particles incombustion chamber 100, which modelling techniques are known to those ofordinary skill in the art. These techniques may, in turn, be used tocontrol biomass feed rate and airflow through primary air distributionand delivery system 110 and secondary air distribution and deliverysystem 130 to effect residence time and the overall combustion processin combustion chamber 100. By way of non-limiting example, in theexemplary prototype construction described below, biomass materialresidence time in combustion chamber 100 would preferably be in therange of 2-5 seconds with combustion temperatures of 1400-1700° F.

FIG. 6 is a top, cross-sectional view of the cyclone combustor 300,having an air inlet 302 that receives flue gas from combustion chamber100 and fresh air from air delivery system 200. The high temperatureflue gas directed to cyclone combustor 300 may contain unburned carbonparticles. As shown in FIG. 6, fresh air is added into the flue gasbefore it enters the cyclone combustor 300. In this configuration, theunburned carbon particles and oxygen in the fresh air will burn again inthe cyclone combustor 300. In addition to re-burning the unburnedcarbon, the cyclone combustor 300 functions as a particle separator inwhich the coarse particles will fall down to a particle collector. Theflue gas is therefore preliminarily cleaned through the cyclone, beforeit is passed on to heat exchanger 400 and exhaust system 500.

As mentioned above, heat exchanger 400 may be employed to put heatcaptured from the flue gas from combustion chamber 100 to useful work.For example, such heat exchanger 400 may be used to produce electricitythrough employment of a Sterling engine or through steam generation todrive a turbine. Moreover, heat exchanger 400 may be used for directheating of water, for drying of materials (including drying of biomassmaterial that is to be processed through combustion chamber 100 beforeits introduction into combustion chamber 100), or for heating of spacesfor workers, consumers, livestock, or the like.

After heat exchanger 400, the flue gas may be directed to exhaust system500, which may include (by way of non-limiting example) a filter bag orother filter housing, and an exhaust stack or exhaust gas pool ofstandard configuration.

The foregoing system may be used to process a wide variety of biomassmaterial, including (by way of non-limiting example) poultry litter,municipal solid waste, agricultural waste, algae waste, biomedicalhazard waste, and the like. Moreover, sawdust, wood chips, wood pellets,switch grass, dried leaves, corn husks, rice shells, and such otherbiomass materials as may be selected by those skilled in the art maysimilarly be processed by the foregoing system to produce high heat andenergy.

The foregoing system may be particularly well suited to processing ofpoultry litter. While total poultry litter production on a given poultryfarm will determine feed rate of materials to combustion chamber 100, ina particularly preferred configuration, poultry litter may be directedto combustion chamber 100 at a feed rate of 40-60 lb/hr. Operating at aschedule of 20 hours/day, 6 days/week, and 52 weeks/year, such a feedrate can process approximately 300,000 pounds of poultry litter eachyear. In processing such poultry litter (as well as other biomassmaterials), it will be important to monitor and regulate moisture of thefeedstock to ensure proper combustion in combustion chamber 100.Particularly for poultry litter, a desired practical moisture level isbetween 15% and 35%, and above this range, pre-drying will be requiredfor combustion to proceed efficiently in combustion chamber 100. Ofcourse, feedstock may certainly have a lower moisture content andachieve proper combustion in combustion chamber 100, such that anoverall operational target is for moisture content of any biomassmaterial to be generally below 35%.

In accordance with certain aspects of the invention, a method forprocessing biomass material may comprise the steps shown in FIG. 7. Atstep 702, biomass feedstock is provided having a moisture content thatis general less than 35%. In the event that such biomass has a moisturecontent higher than 35%, predrying of such biomass material should becarried out to reduce the moisture content. Next, at step 704, suchbiomass material is introduced into a combustion chamber 100 of abiomass combustion system configured as detailed above. As the biomassmaterial is being introduced into combustion chamber 100, as noted atstep 706, a vertical primary airflow is directed into combustion chamber100, while multiple, vertically displaced tangential airflows areintroduced into combustion chamber 100, so as to create a swirlingfluidized bed of the biomass particles in combustion chamber 100, withthe biomass particles being combusted at a combustion efficiency of atleast 90%. At step 708, flue gas from the combustion chamber is directedto a cyclone separator configured as above, where any unburned waste andparticles that were unburned in the combustion chamber are burnedcompletely, and flying ash is divided and collected in a containerconnected to the cyclone separator, while dioxin production issignificantly minimized if not altogether eliminated. The collected ashand char may thereafter optionally be used as fertilizer. Next, at step710, the system exhaust (in the form of high temperature flue gas) isdirected to a heat exchanger, and at step 712 the heat captured from theheat exchanger is put to useful work, such as by generating steam fordelivery to a turbine, powering a Sterling engine, or other such otherenergy generation devices as may be apparent to those skilled in theart, or for direct heating of process materials, such as water, feedstock (for drying the same), or the like, or such other direct heatapplication processes as may be apparent to those skilled in the art.Finally, at step 714, the flue gas is directed from the heat exchangerto the exhaust system with significantly reduced noxious emissions, andmore particularly having NO_(x) of less than 80 ppm, SO_(x) of less than20 ppm, CO₂ of less than 2%, and particulate matter content of less than3 lb/MM Btu.

Example 1

A lab-scale prototype of the system described above was designed andbuilt by the Lee Research Group at The Center for Advanced EnergySystems and Environmental Control Technologies (CAESECT) at Morgan StateUniversity in Baltimore, Md. The lab prototype system can process 11-24lb/hr of pre-dried poultry litter with high combustion efficiency (over96%) without co-combustion or bed materials. The poultry litter wasburned in a well-controlled environment at a temperature low enough(1,400-2,100° F.) to avoid formation of nitrogen oxides, but high enoughto avoid agglomeration and slagging in the ash. Milestones forefficiency, ultra-clean emissions, and particular matter were set asfollows: NO_(x) (30-80 ppm), SO_(x) (15-20 ppm), CO₂ (1.5-2.0%), andparticulate matter (2.0-2.5 lb/MM Btu). The residual fly ash (i.e.,phosphate P₂O₅ and potassium, K₂O) is a high value fertilizer. Theresults produced from the prototype configuration indicate improvedperformance characteristics over other combustion technologies, as shownin Table 1 below.

TABLE 1 Comparison of System with Other Combustion Technologies SystemAccording to Aspects of the Stoker* BFBC* CFBC* Invention FiringCapacity Small/ Small/ Medium/ Small/ Medium Medium Large MediumCombustion =80% 80-90% 85-94% Above 95% Efficiency (%) SO_(x) RemovalNone Sorbent Sorbent in Optional in combustor in bed bed/ freeboardNO_(x) Emissions High Low Very low Very low Ash Form Bottom BottomBottom Fly ash ash ash ash Combustion 1,300 850-950  850-1000  850-1,250 Temperature Primary Air   100 100 >80 10-50 Fraction (%)Mean Gas- None    0.2 0.5-1.0 1-5 Particle Slip Velocity (m/s)Turbulence in None Good Excellent Excellent Combustor *Stoker-FiredCombustor, BFBC—Bubbling Fluidized Bed Combustor (FBC), CFBC—CirculatingFBC, SFBC

In order to achieve the foregoing benefits, the prototype system wasconfigured as detailed in Table 2 below:

Combustor Dimensions Component Description Units (in) Units (cm) 1Combustor Outer Diameter (d_(cod)) 15.12 38.4048 2 Combustor InternalDiameter (d_(cid)) 13.72 34.8488 3 Refractory Material Thickness (t_(r))0.7 1.778 4 Fuel Feeder Diameter (d_(f)) 2.9 7.366 5 Primary Air InletDiameter (d_(p)) 3.5 8.89 6 Secondary Air Inlet Diameter (d_(s)) 0.461.1684 7 Total Combustor Height (H) 74 187.96 8 Air Box Height (H_(a))13 33.02 9 Combustion Chamber Height (H_(c)) 61 154.94

The prototype configuration was provided one primary port and 12secondary ports. The primary air was injected from the bottom of thechamber. The heights of secondary air nozzles were 34, 45 and 55.5 inchrespectively. The feeding rate for the prototype configuration was 11-24lb/hr. The air flow rate for primary air was 49-110 cfm, and forsecondary air was 6-16 cfm. The temperature during poultry littercombustion was between 1,400-2,100° F., which achieved up to 97%combustion efficiency. The measured emissions from the combustionchamber were 0-23 ppm NOx, 0-19 ppm SOx, 0-1.7% CO2, and particularmatter of 0.45-1.19 lb/MM Btu, achieving a combustion efficiency of upto 97%.

A system and method implemented in accordance with the above disclosureprovides significant opportunity for the clean disposal of biomass withthe added advantage of power generation. The total number of farms inthe U.S. producing poultry products, including broilers, breeders andegg layers is estimated at 99,700. Of this total, approximately 30,000broiler farms account for 95% of broiler production in the U.S., with6%-7% of broiler production generated in the Delaware-Maryland-Virginiaregion, with 2,700 broiler farms. The U.S. accounts for 20% of theworld's broiler production, while European Union countries account for12% (60% of U.S.). The current projections for both the small scale farmunit and a large scale regional unit configured as described above wouldgenerate energy to the grid that is currently estimated to be able topay back the capital cost in 3.5 years. This does not include anyenvironmental credits/funding, or the value of cost for bio-wastedisposal.

Longer-term markets would include any agricultural industry wherebiomass is generated and must be disposed of in a clean, cost-efficientmanner (including, by way of non-limiting example, pork and meatproduction industries, rice husk bio-mass, and post algal processed(oil-extracted) biomass). In addition, algae is an interesting source ofbio-energy for its concentration of oil. Currently, after oilextraction, the remaining algal biomass can be dried and “pelletized”and used as fuel that is burned in industrial boilers and other powergeneration sources. The system and method described herein may besuitable to decrease costs of generating energy from the spent algalbiomass, increasing the market potential for the technology.

Moreover, the system and method described herein are believed to providesignificant improvement over conventional direct combustiontechnologies. For example, for bubbling fluidized bed combustion, highpressure air is fed through the bottom of the boiler with lowerfluidization velocity which causes a bubbling effect and allows most ofthe bed material to be retained in the lower furnace. For circulatingfluidized bed combustion, high-pressure air suspends the bed materialand fuel particles, which can rise up the chamber into the cyclone.Heavy particles will fall into the cyclone hopper and be returned to thefurnace to be used again. For swirling fluidized bed combustion,secondary air ports provide a swirling flow environment for combustionin an effort to increase the particle residence time and reduce unburnedparticles. However, the system and method employed in accordance withthe invention provides multiple levels of secondary air injectionnozzles, with optimized configurations for both primary air injectionnozzles and secondary air injection nozzles, which features optimize theability to control the combustion process and achieve higher combustionefficiencies (with resulting lower noxious emissions) than suchpreviously known systems. As demonstrated in the initial test results(above), the system and method disclosed herein 1) provides efficientburning at controlled temperatures which reduces NO_(x) and particulateemissions, 2) supplies sufficient secondary air and extended swirlingair to burn fuels in the upper part of combustion chamber with highefficiency, 3) mixes fuel and combustion air quickly and uniformly, and4) provides large gas-particle slip motion which prolongs particleresidence time and allows a reduction in chamber size and thus the costof the system.

Having now fully set forth the preferred embodiments and certainmodifications of the concept underlying the present invention, variousother embodiments as well as certain variations and modifications of theembodiments herein shown and described will obviously occur to thoseskilled in the art upon becoming familiar with said underlying concept.It should be understood, therefore, that the invention may be practicedotherwise than as specifically set forth herein.

1. A system for fluidized bed combustion, comprising: a combustionchamber, said combustion chamber further comprising: a primary airdistribution and delivery system configured to provide vertical airflowthrough said combustion chamber; and a secondary air distribution anddelivery system configured to provide a plurality of verticallydisplaced, horizontally aligned, tangential airflows in said combustionchamber; and a biomass feeder in communication with an interior of saidcombustion chamber and positioned to deliver biomass material to saidinterior of said combustion chamber at a location above said primary airdistribution and delivery system and below said secondary airdistribution and delivery system.
 2. The system of claim 1, furthercomprising a cyclone separator positioned downstream from saidcombustion chamber.
 3. The system of claim 2, said cyclone separatorhaving an air inlet configured to receive flue gas from said combustionchamber and fresh air from an air delivery system that supplies air tosaid primary air distribution and delivery system and said secondary airdistribution and delivery system.
 4. The system of claim 2, furthercomprising a heat exchanger positioned downstream from said combustionchamber, wherein said heat exchanger is in thermal communication with athermal energy conversion device.
 5. The system of claim 1, furthercomprising a mobile chassis, wherein said combustion chamber is mountedon said mobile chassis.
 6. The system of claim 1, further comprising amonitoring and control system, said monitoring and control systemfurther comprising: a gaseous emissions monitor configured to detectlevels of particular matter and noxious emissions in flue gas from saidcombustion chamber; and a processor having computer executable codeconfigured to: receive data from said gaseous emission monitor; comparedata received from said gaseous emissions monitor to alert levels of anamount of particulate matter and noxious gases in system flue gas; andin response to a determination that said amount of particulate matter ornoxious gases in system flue gas exceed said alert levels, direct acontrol signal to at least said secondary air distribution and deliverysystem to vary airflow through said secondary air distribution anddelivery system.
 7. The system of claim 1, wherein said secondary airdistribution and delivery system further comprises a plurality ofvertically displaced, horizontally aligned sets of air injectionnozzles.
 8. The system of claim 7, wherein each set of air injectionnozzles comprises a plurality of nozzles evenly spaced around aninternal circumference of said combustion chamber.
 9. The system ofclaim 8, wherein each air injection nozzle further comprises a firstbranch extending radially through a wall of said combustion chamber, andan internal branch configured at 90° to said first branch.
 10. Thesystem of claim 9, wherein said first branch comprises an inlet, an airinlet channel extending from said inlet to an interior, circularchamber, an interior flow channel extending from said circular chamberin a direction parallel to but not collinear with said air inletchannel, and a nozzle outlet extending at 90° from said interior flowchannel and having a reducing diameter as said nozzle outlet extendsfrom said interior flow channel.
 11. The system of claim 8, wherein saidsystem further comprises at least three of said sets of air injectionnozzles.
 12. A method for fluidized bed combustion, comprising the stepsof: providing a combustion chamber, said combustion chamber furthercomprising: a primary air distribution and delivery system configured toprovide vertical airflow through said combustion chamber; and asecondary air distribution and delivery system configured to provide aplurality of vertically displaced, horizontally aligned, tangentialairflows in said combustion chamber; providing a biomass feeder incommunication with an interior of said combustion chamber and positionedto deliver biomass material to said interior of said combustion chamberat a location above said primary air distribution and delivery systemand below said secondary air distribution and delivery system; directingbiomass from said biomass feeder to said combustion chamber; directing avertical primary airflow into said combustion chamber and multiple,vertically displaced tangential airflows into said combustion chamber tocreate a swirling fluidized bed of biomass particles in said combustionchamber; and maintaining a biomass feed rate from said biomass feeder, aprimary airflow rate from said primary airflow, and a secondary airflowrate from said tangential airflows sufficient to maintain a combustionefficiency of at least 90%.
 13. The method of claim 12, furthercomprising: providing a monitoring and control system, said monitoringand control system further comprising: a gaseous emissions monitorconfigured to detect levels of particular matter and noxious emissionsin flue gas from said combustion chamber; and a processor havingcomputer executable code configured to: receive data from said gaseousemission monitor; compare data received from said gaseous emissionsmonitor to alert levels of an amount of particulate matter and noxiousgases in system flue gas; and in response to a determination that saidamount of particulate matter or noxious gases in system flue gas exceedsaid alert levels, direct a control signal to at least said secondaryair distribution and delivery system to vary airflow through saidsecondary air distribution and delivery system; and modifying airflowthrough said secondary air distribution and delivery system to maintaincombustion efficiency in said combustion chamber of at least 90%. 14.The method of claim 12, wherein said biomass has a moisture content ofless than 35%.
 15. The method of claim 12, further comprising the stepof directing flue gas from said combustion chamber to a cycloneseparator.
 16. The method of claim 15, further comprising the step ofdirected flue gas from said cyclone separator to a heat exchanger inthermal communication with a thermal energy conversion device.
 17. Themethod of claim 16, further comprising the step of directing flue gasfrom said heat exchanger to an exhaust system.